The complex chromatin-based genomic regulatory system controlling developmental gene expression in complex bilaterians predates the evolution of morphological complexity and may have been a prerequisite for the evolution of the first simple multicellular animals.
Cellularization in Sphaeroforma arctica generates a self-organized structure that morphologically resembles an epithelium, and is associated with tightly regulated expression of cell adhesion pathways.
Sponges and ctenophores lack hypoxia-inducible factors, suggesting that the metazoan last common ancestor could have lived aerobically under severe hypoxia and did not need to regulate its transcription in response to oxygen availability.
The coding sequences of a very highly conserved family of neurogenic transcription factors from different species have evolved to generate proteins that have different life times causing them to display quantitatively different neural induction potentials.
The foundations of genomic complexity in multicellular animals have deep roots in their unicellular prehistory, both in terms of innovations in gene content, as well as the evolutionary dynamics of genome architecture.
A conserved alternative splicing program is specific to planarian stem cells and is controlled by the highly conserved splicing factors CELF and MBNL; therefore, this mode of regulating stem cells is likely ancestral to all animals.